It's a little known fact that your choice of optics in Call of Duty: Black Ops 2 affects your accuracy? And I don't mean to say that your accuracy's affected by the visibility of the reticle or anything of the sort. Rather, it's a gameplay thing—your gun's performance is directly affected by the sight you use.
Since Call of Duty 4, your optical attachments—such as the ACOG Sight and the Reflex/Red Dot Sight—only affected your visual recoil (that Drift0r refers to as the shake on the gun) and nothing else. That's since changed in Black Ops 2. Several of the optics in the game modify the accuracy and recoil of the guns you have equipped.
According to Drift0r, who's done an in-depth report on each of the optics in Black Ops 2, two sights: the EOTech and the ACOG Sight affect the recoil pattern of your gun regardless—this difference is consistent across every gun.
The Variable Zoom and the Dual Band also modify your aiming performance, but the changes differ depending on the gun.
The sights that do not affect accuracy or recoil are the Target Finder, Hybrid Sight, Ballistic CPU, Reflex Sight, Iron Sights, and the MMS. You can stick to those if you care little for the accuracy improvement offered by the sights that do affect your gun's performance. Drift0r notes that the Target Finder has less visual shake, but it doesn't actually affect the performance of your gun. However, it does make it a lot easier for you to aim as a player, as it provides easier identification of opponents in your display.
You can find about all that and more, in the in-depth optics guide by Drift0r below.